Belt tensioners use a system or mechanism to dampen tensioner movement which minimizes steady state vibrations or transient events that cause belt slip. The required magnitude of this damping depends on many drive factors including geometry, accessory loads, accessory inertia, engine duty cycle and others. For instance, drive systems that have higher torsional input or certain transient dynamic conditions may require higher damping to sufficiently control tensioner movement. Although higher damping is very effective at controlling arm movement, it can also be detrimental to other critical tensioner functions (e.g. slow or no response to slack belt conditions). In addition, variation or change in damping that occurs as a result of manufacturing variation, operating temperature and component break-in or wear can also result in undesirable tensioner responsiveness.
Damping derived by utilizing shear forces generated by rotating plates through a viscous fluid has been used with belt tensioners. One particular method involves a rotating plate and a fixed plate surrounded by a viscous fluid as in U.S. Pat. No. 4,838,839 to Watanabe. To achieve the fluid damping in Watanabe, the fixed plates are fixed directly to the fixed shaft, and the displaceable plates are fixed directly to an oscillation sleeve.
Other solutions using plates for hydraulic damping are found in U.S. Pat. Nos. 4,601,683 and 5,391,119 to Foster and Kondo respectively. These designs specifically manufacture the plates to attach directly to the rotating and fixed parts of the tensioner. This approach requires more complex manufacturing and assembly processes.
The aforementioned hydraulic damping mechanisms are not ideal. Accordingly, a new damping mechanism and tensioner design is desired.